This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
Some other mushrooms, like the deadly Amanita (Amanita phalloides) and other species of the genus Amanita, have, in addition to the cap, gills, stem, and ring, a more or less well formed cup-like structure attached to the lower end of the stem, and from which the stem appears to spring. (Figs. 55, 72, etc.) This is the volva, sometimes popularly called the "death cup," or "poison cup." This structure is a very important one to observe, though its presence by no means indicates in all cases that the plant is poisonous. It will be described more in detail in treating of the genus Amanita, where the illustrations should also be consulted.
Of the mushrooms which have stems there are four types with respect to the presence or absence of the ring and volva. In the first type both the ring and volva are absent, as in the common fairy ring mushroom, Maras-mius oreades; in the genus Lactarius, Russula, Tricholo-ma, Clitocybe, and others. In the second type the ring is present while the volva is absent, as in the common mushroom, Agaricus campestris, and its close allies; in the genus Lepiota, Armillaria, and others. In the third type the volva is present, but the ring is absent, as in the genus Volvaria, or Amanitopsis. In the fourth type both the ring and volva are present, as in the genus Amanita.
There are also quite a large number of mushrooms which lack a stem. These usually grow on stumps, logs, or tree trunks, etc., and one side of the cap is attached directly to the wood on which the fungus is growing.
Agaricus campestris. "Buttons" just appearing through the sod. Some spawn at the left lower corner. Soil removed from the front. (Natural size.)
The pileus in such cases is lateral and shelving, that is, it stands out more or less like a shelf from the trunk or log, or in other cases is spread out flat on the surface of the wood. The shelving form is well shown in the beautiful Clandopus nidu-lans, sometimes called Pleurotus nididans, and in other species of the genus Pleurotus, Crepidotus, etc. These plants will be described later, and no further description of the peculiarities i n formof the mushrooms will be now attempted, since these will be best dealt with when discussing species fully under their appropriate genus. But the brief general description of form given above will be found useful merely as an introduction to the more de-tailed treatment. Chapter XXI (Recipes For Cooking Mushrooms) should also be studied. For those who wish the use of a glossary, one is appended at the close of the book, dealing only with the more technical terms employed here.
Agaricus campestris. Soil washed from the "spawn " and "buttons," showing the young "buttons " attached to the strands of mycelium. (1 1/4 natural size.)